Stabilizing and improving qubit coherence by engineering noise spectrum of two-level systems

Abstract

Superconducting circuits are a leading platform for quantum computing. However, their coherence times are still limited and exhibit temporal fluctuations. Those phenomena are often attributed to the coupling between qubits and material defects that can be well described as an ensemble of two-level systems (TLSs). Among them, charge fluctuators inside amorphous oxide layers contribute to both low-frequency $1/f$ charge noise and high-frequency dielectric loss, causing fast qubit dephasing and relaxation. Moreover, spectral diffusion from mutual TLS interactions varies the noise amplitude over time, fluctuating the qubit lifetime. Here, we propose to mitigate those harmful effects by engineering the relevant TLS noise spectral densities. Specifically, our protocols smooth the high-frequency noise spectrum and suppress the low-frequency noise amplitude via depolarizing and dephasing the TLSs, respectively. As a result, we predict a drastic stabilization in qubit lifetime and an increase in qubit pure dephasing time. Our detailed analysis of feasible experimental implementations shows that the improvement is not compromised by spurious coupling from the applied noise to the qubit.

arXiv comment14 pages, 7 figures

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• Systematic Improvements in Transmon Qubit Coherence Enabled by Niobium Surface Encapsulation
• Near-field localization of the boson peak on tantalum films for superconducting quantum devices
• Compact vacuum gap transmon qubits: Selective and sensitive probes for superconductor surface losses
• Analogue Quantum Simulation with Fixed-Frequency Transmon Qubits
• Correlated frequency noise in a multimode acoustic resonator
• Disentangling the Impact of Quasiparticles and Two-Level Systems on the Statistics of Superconducting Qubit Lifetime
• Qubit dephasing by spectrally diffusing quantum two-level systems
• Dynamic phases induced by two-level system defects on driven qubits